Biologic Specialization in the Genus Septoria

BIOLOGIC SPECIALIZATION IN THE GENUS SEPTORIA WALTER SPURGEON BEACH B. S. University of Minnesota, 1914. M. S. Michigan Agricultural College, 1915. THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY IN BOTANY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1918 Digitized by the Internet Archive in 2013 http://archive.org/details/biologicspecialiOObeac UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL DmT X 19lX - I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY. ENTITLED. BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR In Charge of Thesis Head of Department Recommendation concurred in* Committee on Final Examination* *Requireci for doctor's degree but not for master's CWJC Table of Contents Page I. Introduction ----------------------l II. Historical ---------------------- 4 III. Experimental Methods and Material ---------- 9 IV. Septoria polygonorum Desra. -------------- 12 V. Septoria lactucicola E.& M. -------------- 16 VI. Septoria lactucae Pass. ----------------19 VII. Septoria tritici Desra. ----------------23 VIII. Septoria malvicola E.& M. -------------- 30 IX. Septoria scrophulariae Peck --------------32 X. Septoria convolvuli Desra., Septoria septulata sp.nov. 33 XI. Septoria verbascicola B.& C. ------------- 37 XII. Septoria cirsii Niessl. --------------- 40 XIII. Septoria brunellae E.& H. -------------- 42 XIV. Septoria lycopersici Speg. --------------43 XV. Septoria lepidiicola E.& M. --------------45 XVI. Septoria helianthi E11.& Kell. -- -47 XVII. Septoria rubi West. -----------------51 XVIII. Septoria atro-purpurea Peck ------------ 52 XIX. General discussion Age incidence -------------------53 Susceptibility of different leaf surfaces ----- 53 Effect of the mass of inoculum ---------- 54 Effect of wounding ---------------- 54 Variations in the morphology of the fungus - - - - 55 Host limitations ----------------- 56 The value of disease characters ----------57 Biologic specialization --------------7 Page XX. Conclusions 5^ Literature Cited 60 Graph I with Explanation .............. --63 Plate I with explanation ................55 Biographical Sketch -------------------6$ PIOLOCT" 9P7riAT.IZATTO\T T v TH^ GENUS SFPTOPIA T Introduction The genus ?eptoria presents an excellent field for the studv of biologic specialization on account of the very large number ar.d the uncertain status of the described species, cf which there are more than 1200. The morphological characters for the limitation of these are few, consisting chiefly of spore shape, length, thickness, and septation, and in some instances a slight tinting of the spore; pycnidium sh»r*e, size, and color; and os- tiole size and character. The ciclc^ical characters for the limitation of species are the size, shape, margin, conation, and color cf the disease spots, and their location and distribution upon the host. The specific descriptions in many cases are meager and real- ly useless. The presence of a Peptoria upon an unrecorded host is often made the basis of a new species. By tabulating (10), according to spore length, all the "species" of Septoria given in SaccardO 1 a "Sylloge Fungorum", it has been found that nearly 700 fall within the limits of 20 to 50 microns. Twenty-six species on grasses are between 20 to 40 microns. Yet in one esse a Saccardian description gives a spore length rant?- insr from 19 to 62 microns. There have been sreat inaccuracies in measuring spores and pyenidia., with tendencies tc report the meas- urements in round numbers. Elliott (7) has shc*.vn the degree of personal error with our modern technique. Among eleven observers measuring many spores of Alternaria, he found that there was a 2 variation of over 41$ from the highest measurement returned for maximum length, and that such a variation would make it impossible to distinguish the species of Alternaria on the basis of spore measurement. Septation is largely dependent upon the stage of maturity of the spores, is often difficult to see, and was ignored by early mycologists. Enviromental conditions cause fluctuations in the size of spore9 and pycnidia. The value of disease characters is doubtful for they commonly change with the age, the part, and the species of the host, as well as with weather conditions. The confusion that Cavara (4) met regarding these points in his at- tempt to distinguish Septcria t rit ici and S. graminum on wheat, led him to state that both forms probably belonged to the same morphological species. Little is known respecting the existence of biologic specialization in the genus Septcria. Except for a few instances (15, 22, 45) no cross-inoculations have been made to ascertain whether a Septoria, as found upon a particular host, is restricted to that host, or is more or less cosmopolitan and adaptive in its parasitism. In the literature at present one is confronted by two extremes of treatment: (a) closely similar species are described on the same host, e.g. , Sept or ia lactucae and S. consimili s on Lact uca sat iva; (b) more widely variant forms on distantly related hosts are described as representing one species, e.g., S. graminum on twelve or more genera of grasses, and a species of sedfre. It is obvious that such pra.ctice is not consistent, and cannot adequately reflect the truth. The facts as presented above are illustrative of the present unsatisfactory status of the species not only of Septcria but also 3 of many other genera of the Fungi Imperfecti. More accurate knowl- edge regarding host characters, morphological variation, and biological specialization is greatly needed from the standpoint of classification. The genus is the more worthy of studv on account of its high economic importance. To study such a large genus as Septoria in culture, either upon the living hosts or upon arti- ficial media, would require the time of many investigators. The present paper is intended merely as a contribution to the general problem as suggested above, and the investigations were conducted with the following leading objects: 1. to determine the host range of as many species of Septoria as possible in order to ascertain; (a) whether morphologically similar forms from different hosts vary in host range, (b) whether morphologically unlike forms ever have the same host range; or in other words to ascertain whether anv of the species available for study consist of a number of biological forms, and whether any now listed as distinct species are identical. 2. to compare disease characters, i.e., the host response to infection, when produced (a) by a single species of Septoria upon dissimilar hosts, or (b) by different species of Septoria on the same host. 3. to note any morphological changes in the size and shape of spores and pycnidia as a result of change of host or of the condition of the host, or of other environmental factors. 4. to determine the susceptibility of different parts of the same host and of these at different stages of maturity, and to note whether any distinctions in disease characters are correlated with host structure and condition. II Historical The literature dealing with biologic specialization is extensive. A comprehensive review cannot be undertaken here, yet a brief summary of the essential points, especially as brought out bv the investigations of rusts and powdery mildews, will be useful in the interpretation of results to be presented. It may be well to mention thRt biologic specialization is also spoken of as "adaptive parasitism", and biologic forms as "biologic species", "biologic races", "physiological races", and "adapted races. " While Friksson was first to conduct extensive experimental work in biologic specialization, the idea was in the mind3 of earli er investigators for Schro'ter (8, footnote) in 1379 spoke of split- ting up the old species Puccinia caricis into a number of forms differing slightly morphologically, but widely in biologic charac- t eri sties. Eriksson (8) called attention more definitely to the nature of biologic specialization through the results of his cross- inoculation experiments with Puccinia gramlnis in Sweden. He found that, although this rust upon the cereals and grasses represented the same morphological species, the form upon one host-species was not always identical with the form upon another; since, for example oat rust would transfer to oats, but not as a rule to other species of Gramineae. He showed that this fungus embraced at least six distinct forms distinguished by their dissimilar powers of infection with respect to the species of the grass family. In a subse- quent paper (9) Friksson showed that the trend of specialization may be different in isolated localities. This wa3 illustrated by the fact that the form on rye, Puccinia graminis secalis . has a 5 relatively vigorous development in Sweden, but a relatively weak one in North America. In the case of Puocinia graminis trit ici on wheat the more vigorous development is in the latter country. Hitchcock and Carleton (13) performed early infection experiments with Puccinia gramini3 in the United States, and obtained results in agreement with those of Eriksson. Carleton (2,3) in working with biologic forms of rusts has secured valuable data upon varietal resistance in cereals. Ward (46), experimenting with Puccinia dispersa upon Promus, showed the presence of several biologic forms of this fungus on this single host-genus, and discovered "bridging species". The nature of a "bridging species" is described by this statement of the author: "although it is generally true that the adapted races of Puccinia dispersa are restricted to groups of closely allied species, there do occur species which serve as intermediaries in the passage of the fungus from one section of the genus to the other. " Arthur (l) reported that Puccinia helianthi is divided into a number of biologic races, and that Helianthus annuus acts as a bridging host, Stakman (42) in a study of the physiological races of rusts showed that the power of wheat rust to infect rye was somewhat in- creased when the fungus lived a number of generations on barley.

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